Over the years, I’ve resigned myself to the fact that Mother Nature has an intelligence that far surpasses human intellect. For instance, what we think we know about good gardening practices goes entirely down the drain when we examine the interactions of micro-organisms in, or lacking, in our garden soil.

Ignorance, or the absence of knowledge about soil organisms and their functions, is probably the most common condition among average people and gardeners. We know much more about NPK and which chemicals kill insect pests than we know about the beneficial organisms naturally occurring in soil that produce strong healthy plants. The question arises, would you rather try to grow plants in a soil that is heavily doused with chemical nutrients or one that is loaded with fungi and bacteria?

Fact is, a healthy soil is filled with microbial life, some of which we may not yet realize their benefits, and organisms that actually benefit our plants more than any product purchased at the local garden store. The point is, there are things going on out in our soils that we aren’t even aware of… things that we are destroying due to our ignorance or mis-guidance about amending our garden soil.

Overcoming the attitude of “Yeah, I know there are some good soil bugs, but who cares as long as the 10-10-10 is working fine,” might be challenging to some to release. Thankfully, more and more are becoming aware these days. Awareness that real sustainability doesn’t come from a corporation who is highly successful at marketing a line of garden amendment solutions for us to apply every year at the rate specified on the product label.

True sustainability comes from wisdom, knowing through proper information, awareness, and good gardening practices, we do not have to run to the store and buy every miracle bag that lands on store shelves. The cost of these products, the contamination to water they cause, restrictive laws, soil compaction, salt build-up, and many other problems can be easily addressed with down ol’ good wisdom and habits.

“As more and more is learned about how plants really work, it is becoming obvious that the conventional emphasis on soil chemistry and NPK fertilizers has problems – most notably in the areas of drinking water contamination, soil degradation, disease-prone plants, and input costs.”

Plants and Their Allies

In nature, plants can live a good and strong life and mutually-beneficial relationships, a mutual dependence, with many different organisms. Have you ever gone to a national or state park where the land has not been touched by human intervention in decades and witnessed the strong lush growth of the native trees and plants? There’s a reason for this miracle… micro-organisms!

One such organism is mycorrhizal fungi, over millions of years they have formed a mutual dependence with plants. Mycorrhizal fungi are nourished by root exudates and in return bring great amounts of soil nutrients and moisture to their host plants. A plant growing with mycorrhizal fungi can take up 100 times or more nutrients than a plant grown without this beneficial fungi.

Morel mushrooms are both saprobic (decomposing dead organic matter) and mycorrhizal, meaning they also connect to live plant roots in a symbiotic relationship with specialized soil fungi. Together they form root-fungus structures called mycorrhizae. “Mycorrhizae” means fungus-roots. The fungus gets sugars and nutrients from the plant while providing the plants’ roots with a greatly increased absorptive surface area by extending mycelia out into the earth. This enhances the plant’s ability to derive nutrients from the soil.

Almost all healthy plant roots are infected by fungus. The plant’s good health is actually dependent on this fungal infection. Apparently even in rich soil that is sterile, without fungus, most plants can barely survive. It’s the fungal connection that allows them to thrive. This fungal connection is why certain mushrooms are found under certain trees, i.e., Morels in western North Carolina are usually found under Tulip Popular trees.

The difference in a plants health and performance can be dramatic, especially when dealing with less-than-perfect soils. Some extremely dependent plants, such as grapes, citrus, melons, oaks and pines, may quite literally starve to death in soils that lack mycorrhizal fungi.

The same is true for other trees, the mycorrhizal association is beneficial to both the tree and the fungus. The tree supplies carbohydrates and other growth requirements to the fungus, and the fungus increases water and mineral uptake (particularly phosphorus and potassium) of the host tree by increasing the total absorptive area of the root system.

A little field work can reveal this web of growth. Removing the first layer of litter from the forest floor, you can sometimes discern an intricate interwoven mass of white threads. This pale tangle consists of the rootlets of forest trees and strands of fungal mycelia. If you find a fungal thread emanating from a rotting log or decomposing leaf, you may be able to trace it back to a tree’s rootlets.

There are more than 2500 different fungi which form mycorrhizal relationships with trees; often there are several different fungi associated with an individual tree. The presence of this association is necessary for establishment and growth of many trees; its absence has often reduced the success of new tree plantings, especially on old field sites. Mycorrhizae are particularly abundant in forest soils but are found in almost all soils, with the possible exception of grasslands where no trees have previously grown. Growth enhancement is especially significant for plants growing on infertile soils and dry soils.

Heavy Fertilizing Decreases Mycorrhizal Fungi

Interestingly, mycorrhizae development decreases following heavy fertilization of soil. The reduced growth of the pine seedlings in the photo to the right was because of the lack of mycorrhizae on the roots.

The stunted seedlings were those planted in an old limestone rock roadbed. The soil has a pH greater than 8, which the fungus could not tolerate.

Is knowing this changing the way you’re seeing your plants, trees and soil yet? It was a real eye-opener for me when I learned this… this makes so much more sense than adding a myrad of things to the soil thinking I’m doing the right thing. It has absolutely changed the way I look at my soil, plant and tree health. Not to mention, a much deeper appreciation of the natural world. The “Oh my gosh, what have I been doing?!” factor made my gardening actions come to a screeching halt until I could learn more about this fascinating topic.

Kinds of Micro-organisms that Form Close Associations

Fungi

Bacteria, and

A few other groups, such as the actinomycetes.

Don’t Fungi and Bacteria Cause Disease?

A few kinds of fungi and bacteria can cause disease.However, most of them just break down litter, and are not harmful. Some species form these special associations, with direct benefits for themselves and their host trees.

These useful micro-organisms gain…

A ready supply of sugars and other organic substances for energy and growth

A protected place where they can live, and

Extra opportunities of spreading and multiplying.

4 Gardening and Nursery Practices that Affect Mycorrhizas Negatively

Soil sterilization: sterilizing soil at home or in the the nursery generally kills all the beneficial mycorrhizal fungi and decomposers as well as any disease-causing agents, insect pests and weed seeds. If the soil should need to be sterilized (by heating or by chemicals), inoculation with mycorrhizal fungi might well be needed afterwards.

Control of plant diseases: special care is needed with fungicides, or the mycorrhizal partner will be damaged or eliminated. However, they are not all equally toxic to fungi. For instance, it has been found with citrus that thiazole should be avoided.

Insecticides: avoid excessive spraying, and try and prevent the chemical dripping down on to the soil. If any systemic insecticides are to be applied as a soil drench, you might do an informal trial first, and perhaps an experiment to compare different techniques and concentrations (C 15).

Fertilizers: use sparingly or not at all, or you may reduce the likelihood of successful mycorrhiza from forming, or of those that do being effective.

Stop Disturbing Those Who Dwell in the Soil

Adding well decomposed compost (not the cheap bagged materials sold as compost, I don’t know what that junk comes from) is recommended if your soil organic levels are extremely low. After initial compost amending limit further tillage as a good cultural practice. Don’t disturb the soil life, let it thrive and multiply!

Garden Soil is Not Ingredients in a Recipe

Use a broadfork to aerate soil, rather than a roto-tiller. Also avoid turning soil over as this changes the layers in soil which are home to the micro-organisms you “do” want to thrive. Think of it this way… your soil is comprised of many tiny layers, much like in our oceans, in each layer a different set of organisms thrive and multiply. Moving them to a much deeper or more shallow level means their chances of surviving and reproducing are ruined.

The simple act of using a broadfork to loosen compacted soils and scratching compost into the very uppermost layer of soil disturbs the fewest number of beneficial organisms in your soil. I know it’s tempting to want to dig and mix things up well like we’re a human propelled KitchenAid stand mixer. Remember, we are dealing with nature here and she arranged things in such a way that all have an equal chance of surviving and thriving.